In order for an antenna to be effective, it must radiate electromagnetic energy efficiently. That is to say, it must radiate as much energy as possible at the desired frequency, in the desired direction across the desired bandwidth. While antennas can be made to meet these requirements, they often are very expensive to manufacture due to the materials required and the labor necessary to produce them. The size of the antenna also plays an important role in determining which antennas are suited for a particular application. For example, when the application includes an anticipatory collision detection system which operates in the C-band range (4 GHz to 8 GHz) and must be located in the bumper of an automobile, size becomes critical while still maintaining the appropriate beam width and band width. A typical symmetrical horn antenna operating in this range is in excess of one foot in length.
One possible antenna for such an application is a two element patch array. However, this antenna is expensive to manufacture because it requires: expensive microwave materials, a separate printed circuit board which includes an antenna, and a special cover which must be custom tuned very accurately. The antenna must be oriented vertically to produce the desired radiation pattern in the appropriate direction limiting the placement and mounting of the antenna. Even then the beam width is well under 100.degree., requiring multiple antenna sections to produce a usable beam width. Moreover, the usable band width is less than 100 MHz. Thus, this antenna requires multiple manufacturing steps, expensive materials and labor, and yields less than favorable mounting, beam width and band width characteristics.
Another antenna includes the printed circuit dipole or microstrip dipole which has circuits etched on a printed circuit board which is then soldered perpendicularly to the printed circuit board containing the electronics. This results in a flimsy non-rigid structure which also requires a special cover, expensive manufacturing materials and multiple, expensive manufacturing steps to produce and assemble. This structure, like the previous antenna, suffers from similar shortcomings such as a narrow band width, a narrow beam width and a particular orientation which still produces a less than suitable radiation pattern. A typical band width is less than 100 MHz and the beam width is less than 100.degree.. Moreover, this antenna produces high side lobes which, in the case of an anticipatory collision detection system, illuminates the ground increasing system noise, thereby increasing the chance of errors.